1. Technical Field
The invention relates to a phosphor element used for a surface emitting source, a flat display device and the like, and to a display device using the phosphor element.
2. Description of the Related Art
Light emitting diodes, phosphor elements (referred to as EL elements) and the like, are currently used for light emitting devices used in surface emitting sources and flat display devices. Light emitting diodes are phosphor elements that utilize the phenomenon that light is emitted when electrons injected into a p-type semiconductor from a n-type semiconductor are recombined with holes injected into the n-type semiconductor from the p-type semiconductor in an electric field applied to a p-n junction on the junction plane between the p-type semiconductor and the n-type semiconductor. This light emitting diode is quite worthy of evaluation in the point of high emission and high efficiency. In one example of a method of producing this emitting diode, thin layers are laminated sequentially on a semiconductor substrate by crystal growth, as shown in Japanese Patent Laid-Open Publication No. H07-66450. Here, because the light emitting diode emits light from the p-n junction part, the substrate on which these thin layers are grown is diced to expose the p-n junction part as the end face from the surface, thereby taking out the emitted light outside. Therefore, the light emitting diode is a point source of light. In the case of intending to obtain surface emission by using this light emitting diode, plural light emitting diodes are arranged to attain surface emission.
On the other hand, the EL elements are roughly divided into an organic EL element provided with a phosphor material made of an organic phosphor material to which d.c. voltage is applied to recombine electrons with holes to emit light and an inorganic EL element which is provided with a phosphor material made of an inorganic material to which a.c. voltage is applied to thereby collide electrons accelerated in an electric field as high as 106 V/cm with the emission center of the fluorescent body to excite the inorganic phosphor material, thereby allowing the inorganic phosphor material to emit light when this excitement is relaxed.
Explanations will be furnished as to an EL element called a distributed type EL element among inorganic EL elements. The EL element is structured by laminating a first electrode, a phosphor layer, a dielectric layer and a second electrode in this order on a substrate. The phosphor layer contains inorganic fluorescent particles, such as ZnS and Mn dispersed in an organic binder. The dielectric layer has a structure in which a ferroelectric material such as BaTiO3 is dispersed in an organic binder. An a.c. power source is disposed between the first electrode and the second electrode. Then, a.c. voltage is applied across the first and second electrodes from the a.c. power source to make the EL element emit light. For example, Japanese Patent Laid-open Publication No. 2002-216968 discloses a structure in which the aforementioned EL element is covered with a moisture-proof body. The EL element is scarcely limited by the material of the substrate and for example, a plastic film or glass can be used, which makes it easy to develop a larger area semiconductor by using a single substrate.